This invention relates to ice detectors and, more particularly, to an ice detector for determining location and thickness of ice build-up on an aircraft propeller.
Various forms of ice detectors for use with aircraft have been developed. Such detectors include radiometric devices broadcasting in the 35-95 GHz frequency band and relying on frequency shifts in reflected waves such as is disclosed in NASA Contract NAS8-33800 on "Ice/Frost Detection System Using Millimeter Wave Radiometry". Another form of millimeter wave detection is described in NASA Contract Report 3598 entitled "Development and Test of a Microwave Ice Accretion Measurement Instrument (MIAMI)". This latter device uses a resonant surface-mounted transducer whose resonant frequency varies in proportion to thickness of an overlying ice layer. A microcomputer monitors the resonant frequency of the transducer to provide a continuous indication of ice thickness. The transducer is described as a resonant wave guide. Still another ice detector, described in NASA publication 86346479, also identified as NASA-CASE-LAR-13403-1, "Ice Detector", uses a pair of capacitance gauges in combination with a temperature gauge mounted in a cavity on an aircraft structure. The temperature gauge provides an indication of the state of any overlying water, i.e., solid or liquid, while the capacitance gauges provide an indication of thickness.
The above-identified ice detectors have not been fully satisfactory, as is evident by the extent of ongoing research into alternative devices. For example, radiometry requires an essentially stationary surface, and a large power source and antenna for illuminating the surface to be viewed. The resonant wave guide is an intrusive device and requires a directly coupled power source which may be acceptable in surfaces that are not essential to structural integrity but could detrimentally affect structural integrity in applications where such surfaces are essential to structural integrity. Similarly, use of capacitance and temperature gauges requires intrusion into a surface and some form of direct connection for readout The application of any of these systems to high-speed rotating aircraft propellers could therefore present unsolvable problems.